Umbrella devices in the form of umbrellas and parasols are known, whose umbrella-like cap is provided with ribs, one end of which is linked to a ring arranged at the upper end of a shank and the other end at a sleeve, which can be displaced and fixed in place along the shank for spreading the umbrella cap.
These ribs are required for supporting the cover material used as the covering. In case of umbrella devices of larger dimension, the ribs already constitute a large proportion of the dead weight of the umbrella device. With a filigreed weight-reducing design they are prone to buckling when strained by wind. The controlled folding up of the cover material and of the rod produces strain has been shown to be technically difficult with umbrella devices of large surface areas, and poses the danger of damage to the thin cover material of low flexural strength in the contact points between the cover and the ribs.
An umbrella device having a shank and an umbrella-like cap which can rotate around the shank and opened up is known, for example, from U.S. Pat. No. 5,020,557 and from European Patent No. EP-A 0 382 122. In the first case, the umbrella-like cap is rotatingly held for absorbing and compensating wind forces. In the second case, the umbrella-like cap has two elements arranged on top of each other, wherein the upper cap element can be manually rotated with respect to the lower, fixed-in-place cap element by preselected degrees of angle for filtering out undesirable sunlight components. Such umbrella devices with a manually rotatable cap are relatively expensive to produce and elaborate in use, since they can be opened up-only over provided ribs, which moreover have a considerable weight.